Known hydraulically-actuated fuel injection systems and/or components are shown, for example, in U.S. Pat. No. 5,423,484 issued to Zuo on Jun. 13, 1995 and U.S. Pat. No. 5,492,098 issued to Hafner et al. on Feb. 20, 1996. In these hydraulically-actuated fuel injectors, a spring biased needle check opens to commence fuel injection when pressure is raised by an intensifier piston/plunger assembly to a valve opening pressure. The intensifier piston is acted upon by a relatively high pressure actuation fluid, such as engine lubricating oil, when a solenoid driven actuation fluid control valve opens the injector's high pressure inlet. Injection is ended by deactivating the solenoid to release pressure above the intensifier piston. This in turn causes a drop in fuel pressure causing the needle check to close under the action of its return spring to end injection.
Engineers have observed that engines using these fuel injectors can sometimes exhibit unsteady behavior when operating at idle conditions. This unsteady behavior reveals itself as an oscillating rpm at idle conditions, which corresponds to when the fuel injectors are commanded to inject their lowest quantity of fuel. It has been found that the quantity of fuel injected from the injector is very sensitive to fluctuations in the common rail supplying actuation fluid to the injectors as well as variations in the actuation control valve motion. Normal fluctuations in the common rail pressure can result in significant variations in the injected fuel quantity at idle conditions.
Since the injector's solenoid is energized for such a short amount of time at idle conditions, injection quantities can also vary due to the irregular poppet valve motion. In this second instance, small variations in the commanded on-time can itself cause variations in injected fuel quantity. Also, on-times that are insufficient to move the actuation poppet control valve to stop at its upper seat before being commanded to close can also result in variations in injected quantity. In other words, slight variations in the solenoid on-time can cause the poppet valve to bounce off its upper seat and close more quickly than it might for a slightly shorter on-time. Since unsteady engine performance is very undesirable, especially at idle conditions, there is a motivation to make these hydraulically-actuated fuel injectors less sensitive to fluctuations in rail pressure and/or poppet control valve motion variations.
The present invention is directed to overcoming one or more of the problems as set forth above.